1. Field of the Invention
The present invention relates to a method of pneumatic drying disintegrated fiber mass which includes cellulose fibers and is intended for use in the manufacture of paper products.
2. Description of the Prior Art
In conventional drying of cellulose fiber mass or paper pulp, the fiber mass which is in the form of a slurry is applied to a dewatering press in which the fiber slurry is drained and formed to a web which is thereafter exposed to a flow of hot air or passed over steam heated cylinders. Due to relatively slow diffusion of water in the compact web-shaped fiber mass a relatively long drying period is necessary in order to reduce the moisture content to the value desired.
During recent years cellulose fiber mass has also been dried by a pneumatic drying process which is known as a flash drying process. By such flash drying the fiber mass to be dried is supplied into a flow of relatively hot drying air in a disintegrated condition. Due to the fact that a relatively great surface of the disintegrated fiber mass is contacted by the drying air and due to the relatively high drying air temperature which is normally between 250.degree. and 400.degree. C, a relatively short drying period may be obtained by a flash drying process. After drying the fiber mass may be separated from the drying air, for example by means of a cyclone.
The dried fiber mass may be pressed into bales and shipped to customers or consumers such as paper manufacturers. When the dried fiber mass is to be used for making paper, paper board, or other paper goods the fiber mass is suspended in water and subjected to a grinding process.
It has been found that under certain conditions flash dried cellulose fiber mass is more difficult to grind than corresponding cellulose fiber mass which has been web dried in a conventional manner. That means that in order to obtain the same characteristics of the final product a higher amount of power is required for grinding flash dried fiber mass than for grinding web dried fiber mass. This fact has apparently counteracted a more widespread use of flash drying in connection with cellulose fibers to be used in the paper industry.